I was wondering the same thing .... so I ended up calling them last week.
And here is how it works...
Log into your Rogers account online. Once you are in the "My Rogers" page, click on the "Products & Services" tab.
On that screen, there will be a link (towards the middle of the page) to apply for the hardware credit. You just need to click on that and press submit button on the subsequent page (If remember it correctly).
Then they'll send you an email informing you that a credit has been applied to your account. Hope this helps.